Netherton syndrome (NS) is one of the most severe heritable skin disorders of neonates, with life-threatening symptoms that result from a defective skin barrier. Severe complications in infants include recurrent bacterial infections, dehydration, and failure to thrive. In adults, NS is a chronic, debilitating condition with no effective treatmet. Current therapies (anti-inflammatory drugs, immunosuppressants, antibiotics, and drugs for symptomatic relief) are only modestly effective, and often cause unacceptable adverse events, particularly with long-term use. Recently, the cause of NS was identified as mutations in an epidermal protease inhibitor, LEKTI. At neutral pH, in the deep stratum corneum (SC), LEKTI binds and inhibits Kallikrein-5 (KLK5). In normal epidermis, LEKTI inhibits KLK5 through a pH-dependent interaction. In the superficial SC, where the pH is 4.5- 5, this complex dissociates, permitting KLK5 to proteolytically activate additional epidermal kallikreins, KLK7 and KLK14 as well as elastase-2 (ELA2). These proteases degrade corneodesmosomal proteins, leading to shedding of superficial cells. Recent data from human genetic studies, animal models, and siRNA knockdown of LEKTI in organotypic human tissue culture, establish unregulated KLK5 activity as the underlying cause of NS. An inhibitory antibody to KLK5 can provide an effective treatment for NS by blocking the KLK5 protease cascade in the SC. During this Phase I project, we will identify an inhibitory anti-KLH human monoclonal antibody (humAb). We will evaluate inhibitory activity in vitro, using an organotypic human skin culture model. This work has the potential to result in a new therapeutic for NS, by alleviating the life-threatening skin barrier deficits in the newborn, and reducing skin irritation and inflammation in adults. This humAb may also be effective against other dermatological disorders, including atopic dermatitis, that involve activated KLK5.